It is common in shrimp-processing plants to transport raw shrimp from the loading dock to peeling machines at least part of the way by means of a transport system comprising pipes carrying a fluid conveying the shrimp. Typically the shrimp are conveyed through the pipes before finally making their way to the peelers generally intact, i.e., with heads still attached. Conventional peelers, such as those having counter-rotating rollers exemplified by the Laitram Model A Peeler manufactured by the assignee of this invention, detach the head, shell, and appendages from the shrimp meat, which is then segregated from the refuse and packed for sale. When maintained and cleaned properly, such peelers are effective at peeling shrimp. If not properly cleaned, however, eggs carried in the underbelly and visceral matter and fluids principally residing in the head cavity of the shrimp coat the roller sections of the peeler, inhibiting the positive engagement of the peeler's rollers and the grip of the peeling rollers on the shrimp thereby degrading peeling effectiveness. One way the problem has been avoided by the prior art is through the use of knurled peeling inserts and faster roller rotation to effect a more aggressive peeling action, but with a concomitant loss in the yield and quality of peeled tail meat. Another way to avoid the problem is to slow the advance of shrimp along the peeling channel, which decreases production throughput and yield. Another problem with peeling machinery is that grit and sand trapped in the head cavity, legs, and swimmerets of the shrimp abrade the surfaces of the peeling rollers, thereby decreasing their useful lifetimes. Furthermore, the spike-like thorns protruding from the shrimp heads damage the surfaces of the rollers as the shrimp are dropped into the channels for peeling.
In some peeling applications, particularly in the peeling of cold-water shrimp, the shrimp product is cooked prior to peeling. One of the difficulties encountered in precooking shrimp is achieving evenly cooked shrimp with prior art cooking methods. Because the thickest part of the tail meat is next to the body-fluid-heavy head, which acts as a thermal insulator, cooking is uneven. Furthermore, cooking energy is expended in cooking the heads, which are ultimately discarded anyway.
In many shrimp-peeling operations, especially where water usage is restricted, recirculation of the water used to urge the shrimp along the peeling and other processing machines is critical. Eggs and visceral material from the head are typically carried in the recirculated water. This waste material fosters the accumulation of bacteria and diminishes water clarity. Such dirty water is more likely to foul the water recirculation system and require more frequent maintenance.
At sea, it is not uncommon for shrimpers to cull small shrimp from a mixed catch and discard the small ones overboard, because the cost of storing them on board is greater than their market value. Furthermore, more shrimp could be stored, and with less chance of bacterial contamination, if the heads are removed prior to storage.
The removal of heads from shrimp by means of hydrodynamic forces is shown in U.S. Pat. No. 3,309,732, issued Mar. 21, 1967, and U.S. Pat. No. 3,408,686, issued Nov. 5, 1968, to Fred W. Stephenson. All of the Stephenson patents teach the deheading of shrimp by injecting the shrimp into a high-speed stream from outside the stream and using stationary structure in the vicinity of the injection point to act as a decapitating edge. Thus, the Stephenson inventions require an edge jutting into the high speed stream. Furthermore, in the Stephenson apparatus, the stream upstream of the decapitation edge does not transport shrimp. A later Stephenson patent, issued Sept. 15, 1987 as U.S. Pat. No. 4,692,965, represents an improvement on his earlier inventions that decapitates by presenting shrimp singly and oriented tail first to a high-speed stream. Besides having the same characteristics as the deheader shown in the earlier patents, the improved deheader is designed to decapitate one shrimp at a time. The improved Stephenson deheader is typically used to produce deheaded, unpeeled shrimp. As a consequence, 100% decapitation is his goal. In commercial embodiments of the improved Stephenson deheader, the goal is attained by sacrificing some meat severed from the throat portion of the shrimp. In other applications wherein peeled, rather than unpeeled, shrimp is the end product, such a sacrifice of meat is undesirable.
Consequently, some of the objects of the present invention not achieved by the prior art include: a) increasing the throughput of peeling machines without sacrificing product yield or quality; b) increasing the useful life of peeling rollers; c) improving the clarity of recirculated peeling water; d) improving storage efficiency and quality for space-limited applications; and e) enabling shrimp to be cooked prior to peeling more uniformly and energy-efficiently.